The present invention relates to seals for rotating shafts, and more particularly to a bellows-type shaft seal having a self-damping construction.
High speed fluid handling machinery such as rotary pumps, compressors and mixers often employ face seals between a rotating shaft and stationary supporting structure surrounding the shaft. One version of these seals includes a hard annular member or ring which rotates with the shaft and sealingly engages a radial face on the stationary supporting member. The ring surrounds the shaft and is biased into sealing engagement with the radial face by a flexible annular bellows which also surrounds the shaft and forms part of the seal.
In another version, the hard annular ring is sealingly carried by the stationary supporting member and is biased into sealing engagement with a radial face of a member fixed to the shaft by a flexible bellows which forms part of the seal between the ring and the stationary member.
One of the problems with seal assemblies of this type, particularly the version which utilizes a bellows and ring which rotates with the shaft, is that during use, vibrations are induced in the bellows as a result of face friction between the rubbing seal parts, dry running or cavitation, fluid pressure pulsation or turbulence, vibration of other parts, etc. This causes the bellows to become work-hardened and lose its resiliency. Moreover, the bellows is, in effect, a spring, and if it is caused to vibrate in a harmonic mode, it can fracture. Many attempts have been made to overcome the problems resulting from induced vibration in seals of this type but, in general, they are not satisfactory in their performance or they result in an expensive construction.